A known image reading device includes an automatic document feeder (ADF) which has a cover member that covers components such as rollers. The cover member has an outer surface constituting one of exterior surfaces of the image reading device, and an inner surface having ribs that protrude from the inner surface.
Some of the ribs function as sheet passage ribs extending in a sheet conveyance direction in which sheets are conveyed. A space serving as a sheet conveyance path is provided below the lower ends of the sheet passage ribs. When sheets are being conveyed, the sheets are guided through the space.
Some of the ribs other than the sheet passage ribs function as reinforcing ribs extending in a direction orthogonal to the sheet passage ribs. The reinforcing ribs enhance flexural rigidity of the sheet passage ribs and also enhance flexural rigidity and torsional rigidity of the cover member in collaboration with the sheet passage ribs.